Ammoniacal ammonium nitrate solution of reduced corrosive tendencies



United States Patent AMMONIACAL AMMONIUM NITRATE SOLUTION 0F REDUCEDCORROSIVE TENDENCIES Paul Shapiro, Chicago, Ill., David B. Sheldahl,Griflith,

Irld., and Lawrence V. Collings, Park Forest, Ill., asslgnors, by mesneassignments, to Sinclair Research,

Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Feb.1, 1960, Ser. No. 5,637 16 Claims. (Cl. 71-59) The present inventionrelates to the corrosion of ferous metals. More specifically, thepresent invention reates to a novel composition having reduced corrosion.endencies toward ferrous metal surfaces.

There is a well recognized corrosion problem in iniustries concernedwith the manufacture, storage, trans- )ortation and handling ofammoniacal-ammonium nirate solutions. In the handling of such solutionsit is Jften necessary to transport and store them in ferrous :ontainerssuch as drums, tanks and pipelines. In view )f the corrosive nature ofammoniacal-ammonium nitrate iolutions against ferrous metals, manymanufacturers w use storage and transportation facilities constructed )faluminum. Aluminum is used because its oxide film 'enders the metalinert to attack by the ammoniacal salt l0llltl0l'1. This remedy,however, is a costly one. Corosion inhibitors of one type or anotheralso have been :uggested and attempted with varying degrees of limitedBUCCCSS.

One effective method for remedying the problem has new to deactivate theferrous metal, for instance, by passivating the metal surface. Passivityis a property :xhibited by some metals whereby they become inacivetoward certain chemical reagents. When a piece of 'eactive metal is madepassive, its position in the electro- :hemical series is changed so thatit is cathodic to a iece of the same metal which is in the activecondiion. "Passivation of ferrous metals employed in a xxrrosiveenvironment, is generally accomplished by conacting the metal with anoxidizing agent. The oxidizing lgent reacts with the ferrous metalforming a thin adlerent oxide film on its surface. This protective film:hields the ferrous metal from its environment and virtutlly nocorrosion occurs.

Passive films produced by contacting ferrous metal with LQUCOUSsolutions of oxidizing agents are found to be ery fragile and easilydestroyed by mechanical damage, :hemical attack or electrolyticreduction. Hence, the lddlllOIl of a supplementary inhibitor has beennecessary 0 provide protection when the passive film is destroyed. Wehave found, however, that some proprietory inhibiors, i.e. inhibitorscontaining reduced sulfur, e.g. -IH SCN, that are efiective inhibitorswill frequently detroy the passive film.

Moreover, most passivation procedures require a twotep process, i.e. theferrous metal must be first imnersed in an aqueous solution of theoxidizing agent beore it can be exposed to the ammoniacal solution. Thiss done for two reasons, (1) corrosion of the ferrous netal in theammonia-ammonium nitrate solutions is exremely rapid resulting in theformation of a gelatinous leposit on the metals surface preventingaccess of the oxilizing agent to the surface and (2) the oxidizing agentnay be destroyed by reaction with ammonia present in he solution formingnitrogen and its oxides.

It has now been discovered that contacting a ferrous netal withammoniacal ammonium nitrate solutions conaining a soluble coppercompound, a soluble trivalent lrsenic compound and carbonate ionsproduces a tough vassive film on the ferrous metal that otters improved:orro'sion resistance to the metal. It has also been found hatammoniacal ammonium nitrate solutions containing 3,096,169 Patented July2, 1963 the above components, i.e. copper, trivalent arsenic, andcarbonate ions, produce in situ a passive film on ferrous metal that ishighly resistant to mechanical damage and electrolytic reduction, aswell as chemical attack.

The copper compounds in the present invention are the soluble coppercompounds as, for instance, the inorganic compounds such as cupriccarbonates, hydroxides, sulfates, nitrates, etc. Of the many carbonateion-producing compounds, the more particularly suitable are theinorganic compounds, for instance, alkali metal and ammonium carbonates.Preferably, the copper and carbonate components of the present inventionare provided by a single compound such as basic copper carbonate.

The quantity of the aforementioned components employed in the presentinvention can vary considerably but are sufficient to give significantprotection against corrosion. Gene-rally, the concentration of thecopper component is at least about .01 g. per 100 ml. of ammoniacalsolution. The maximum amount of the copper compound is limited only byeconomic feasibility and is generally not greater than about 0.2 g. per100 ml. of ammoniacal salt solution. The preferred concentration isabout .05 to .15 g. per 100 ml. of ammoniacal solution. The amount ofcarbonate compound employed is usually that sufiicient to provide acarbonate ion concentration of at least about .005, generally about .02to .l g. per 100 ml. of ammoniacal solution. When basic cupric carbonateis employed, a concentration of about .01 to 0.2 gram/100 ml. ofammoniacal solution, preferably about .05 to .15, is usually suflicient.

The trivalent arsenic component of the present invention can be providedby a solution of any soluble trivalent arsenic compound, preferably asoluble inorganic trivalent arsenic compound. Inorganic trivalentarsenic compounds that can be employed include, for example, arsenictrioxide, an arsenite such as sodium, potassium or ammonium arsenite andsulfies of trivalent arsenic. Since As O dissolves slowly when added tosolutions such as ammoniacal ammonium nitrate, it is desirable to firstdissolve the compound in alkaline solution such as an aqueous solutionof sodium hydroxide, sodium carbonate, ammonia, etc. Like the coppercompounds, the arsenic compound may vary in amount, but is sufiicient toaiford the desired corrosion inhibition. Generally, the concentration oftrivalent arsenic compound is at least about 0.01 g./100 ml. ofammoniacal solution, usually less than about 0.5 g./100 ml. andpreferably about .05 to .25 g./ 100 ml. It is preferred that thecomposition of the present invention also contain small effectiveamounts of alkali metal, eg. sodium, hydroxide which can be convenientlyprovided in the composition as aforementioned, by employing an aqueoussolution of the sodium hydroxide to dissolve the trivalent arseniccomponent. The amount of alkali metal hydroxide employed will usually beas stated before for the arsenic compound. In providing the ammoniacalammonium nitrate solutions with the components of the present invention,we prefer the absence of significant amounts of halogen ions, e.g. Cl,which are known to be passive film destroyers.

Ammoniacal ammonium nitrate solutions may vary considerably incomposition. Generally representative of such solutions encountered inindustry and which give rise to the corrosion problem discussedhereinbefore, are those having approximately about 1 to percent ammoniumnitrate, usually at least about 40 percent, preferably about 60 to 70percent, about 5 to 35 percent free ammonia, preferably about 10 to 35percent, and the substantial balance being Water, for instance, about 10to 65 percent water. These percentages are by weight.

It has been noted that the corrosion by ammoniacal solutions is intensein the vapor zone, i.e. the portion of the vessel containing theammoniacal solution which is in contact with vapors of the solution.Although the combination of components of the present invention providesgood corrosion protection to the portion of the vessel in contact withthe ammoniacal solution, adequate procharacteristics of a ferrous metalsuch as steel, i.e. makes the metal more electropositive, the phenomenoncan be effectively studied by observing changes in the single electrodepotential of the metal. A series of simple electrd tection is not alwaysprovided the portion in contact with 5 lytic cells were set up toachieve this end. vapor. This problem can be easily remedied by theaddi- A steel rod was first activated (i.e. all surface films tion ofvapor phase inhibitors such as urea, NH NO were removed) by exposure to15% HCl at 150 F. until etc. We have also found that the addition of NO{hydrogen bubbles were observed. The rod was then producing compoundssuch as an alkali metal nitrite to washed in deionized water and placedin an electrolytic the ammoniacal solution containing the components of10 test cell filled with an ammoniacal solution consisting of thepresent invention very effectively reduces vapor phase 66.8% NH NO 16.6%NH and 16.6% H O. The eleccorrosion and this may be due to the formationof a trolytic test cell was a large mouth 8 ounce glass jar hav- CuNH NOcomplex. The vapor phase inhibitor is gening a salt bridge comprising aglass tube with agar-agar erally present in an amount sufficient toprovide adequate solution saturated with KCI connected to a calomel cellrr si n pr and n ly i ab 5 to 15 immersed in saturated KCi. The calomelelectrode probe 0.5 g./1OO ml. of ammoniacal solution. and theactivated" rod were connected by leads to a The following examples areincluded to further illu Sheppard potentiometer by which potentialmeasurements trate the invention. were obtained. Similar tests wereconducted on the am- EXAMPLEI mania-ammonium nitrate solution containingsmall con- As aforementioned when a piece of active metal is made 20 ofVarious oxidiziflg agents combination passive, its position in theelectrochemical series is of oxldlzlng agentsmvalent arsefllc compfmndschanged so that it is more cathodic to a piece of the same Where p ywere 10 each case fil'st dlssolved Wlth all metal which is in the activecondition. Since the formaequal Weight of Sodium hydroxide in diluteaqeuolls tion of passive films produces a change in the electrical tion.The results are shown in Table I.

Table I PASSIVATION OF STEEL IN NHz-NILNO; SOLUTION USING OXIDIZINGAGENTS Concentration T t oxidizing agent 21100 in N NHr-NILNO:

solution Observed single electrode potontini of steel (volts to caiomel)Observations -0.74 0.42 to -0.72 (1 hour.)

0.46 to 0.73 (11 minutes)...

0.76 0.47 to 0.73 (4 minutes) --0.46 to -0.7s (1 minutes) 0.30 to 0.35-(].35 to 0.45

0.29 to 0.20 0.37 to 0.34

0.36 to 0.74 (15 miuutes).... 0.37 to -0.16

Steel corroded, appearance of a slimy green ppt. on the steel surface.Slow corrosion. Rapid corrosion.

Do. Do.

Do. Do.

Rapid corrosion, brown ppt. (due to formation of Mn0;) Rapid corrosion,not too soluble. Slow corrosion.

Rapid corrosion.

Slow corrosion. Passive, metal bright and clean.

Do. Do.

Passive, metal bright and clean, large white ppt. forms,

probably insol. AsiOr.

Passive, metal bright and clean. Passive, metal bright and clean, largewhite ppt. forms,

probably insol. AS505.

Steel corroded.

asslve.

Rapid corrosion.

. Passive.

Rapid corrosion.

lllS (I HQIOOr -0.50 to 0.71 (2D mlnutes) -0.76

Table IContinued Concentration Pest Oxidiziug agent g./1D0 ml. Observedsingle electrode po- Observations 10. NHr-NH4NO3 tential of steel (voltsto calomel) solution 1--.. CuS 0.1 0.39 to 0.28 Passive.

plus (N H0300:

plus AS103 Cu(NO=J, 0.40 to 0.29 Do.

plus (NH4)1CO:

plus

0.76 0.49 to 0.75 (5 minutes) Rapid corrosion. Slow corrosion.

Rapid corrosion.

Do. Slow corrosion.

Table I above indicates that most oxidizing agents when added to NH NHNO solutions produce untable if any, passive films on exposed steelsurfaces, due pparently to their reaction with ammonia. Na Cr O O (NH SO and the basic cupric carbonate-trialent arsenic combination apparentlyare not too reactive tact through the external circuit was maintainedwith the steel. If after five minutes the Flade potential was notexceeded, the copper wire was then brought into physical contact withthe steel. Ordinarily this procedure was suiiicient to destroy the film.Table II below contains the results of this test.

Table II EFFECT OF CONTACT WITH A 2", #12 Cu WIRE ON THE SINGLEELECTRODE POTENTIAL OF STEEL (VOLTS TO CALOMEL) Test Cone. g./100 ml.Time Time, Physical contact Time,

No. Oxidizing agent N1-I NH4NO= exposed, Electrical contact min. (wiretouches rod) min.

solution hours An (NliqhSzOs .l 0. 15 23.0 0.21 to (].78.. 0. 5

B (NIlImSme 0.1 26.0 0.30 to -0.77. 0. 75

0:1 25.5 -0.35 to 0.56 5. 0 0.56 to 0.75 2.0 0.1 26. 0 0.46 to -0.60 5.0 0.(i0 to 0.71 9.0

0. 1 0.1 26. 5 -0.44 to -0.59 5.0 0.59 to 0.73 2.0

23. 5 0.28 to D.58l. 5.0 -0.58

g1} 27 -0.2a to o.59, -.59 to 0.436 0: 1

1 More than 9 days.

vith the solution and produce passive films in situ. The ame is true intests 33 and 34 where copper, carbonate nd arsenic were supplied inanother manner.

The decay of passivity can be observed by recording he decrease inpotential when a metal cathodic to the assive steel is brought intoelectrical contact with it. .he potential shift in the more activedirection (i.e., nore electronegative) is due to the electrolyticreduction if the film by the current that is created by the galvanicouple. When passive steel is activated there is first a teep fall of thepotential in the active direction; second, y a less step change lastingfor a fraction of a minlte to several minutes; and third, by a steepdescent o the active value (i.e., complete breakdown of the iassivefilm; 0.71 to -0.77 volts to calomel for -IH --NH NO The value of thepotential immedittely preceding this last descent is called the Fladcotential.

To determine the resistance to electrolytic destruction if the passivefilms produced by the above reagents, an lctivated steel rod was firstexposed for about a day to JH NH NO solution containing the oxidizingagent 0 that it might become passivated. Then a two-inch niece of No. 12copper wire was placed in the test soluion with the passive steel.Initially only electrical con- 9 More than 6 days.

Table II indicates that the basic cupric carbonatearsenite combinationproduces a very highly stable and resistant passive film when introducedto ammonia-ammonium nitrate solutions. The combination is also efiectivein repairing any breaks in the film. A deep scratch was cut on the faceof the coupon. The coupon was then reinserted in the ammonia-ammoniumnitrate containing the basic cupric carbonate-arsenite combination. Thecoupon was kept in the ammoniacal salt solution for over 2 weeks with novisible signs of corrosion. A good result was also obtained with anothercopper, arsenic and carbonate composition in test H.

In summary, the addition of the inhibitor combination of the presentinvention to corrosive solutions such as ammoniacal salt solutions willinhibit the corrosion of ferrous metal apparatus in which thesesolutions are handled, stored, etc. This will result in greater productpurity and reduce the destruction of shipping and storage facilitieswhich are used commercially such as in the fertilizer business. Thisadvantage can in turn enable manufacturers of these corrosive solutionsto use less costly equipment for handling these solutions. Further inmany corrosive solutions like ammoniacal salt solutions, the cupriccomponents of the present invention produces a clear solution with anintense blue color,

which color can be used to show that a controlled and adequateconcentration of inhibitor is present. In addition, copper is one of thetrace elements required for normal growth of many plants. Hence,incorporation of the cupric compounds of the present invention inammoniacal fertilizer solutions may enhance their Value as fertilizers.

We claim:

1. A composition consisting essentially of an aqueous ammoniacalammonium nitrate solution, about 0.01 gram to less than about 0.5 g./100ml. of said solution of a trivalent arsenic compound, soluble in saidsolution, about 0.01 to about 0.2 gram/100 ml. of said solution of acopper compound soluble in said solution, and about .005 to .1 gram/100ml. of said solution of carbonate ions, the amounts of said compoundsand ions being sufficient to substantially reduce the rate of corrosionby said solution to ferrous surfaces.

2. The composition of claim 1 in which there is in cluded a small amountof alkali metal hydroxide.

3. The composition of claim 2 in which the hydroxide is sodiumhydroxide.

4. The composition of claim 1 wherein the concentration of the trivalentarsenic compound is about 0.05 to 0.25 gram/100 ml. of said solution,the concentration of the copper compound is about .05 to .15 gram/100ml. of said solution and the concentration of the carbonate ions isabout 0.02 to .1 gram/100 ml. of said solution.

5. The composition of claim 1 where the copper and carbonate ions aresupplied by basic copper carbonate.

6. The composition of claim 3 where the copper and carbonate ions aresupplied by basic copper carbonate.

7. A composition resistant to corrosion of ferrous surfaces consistingessentially of an aqueous ammoniacal ammonium nitrate solution of about40 to 80% ammonium nitrate and about to 35% ammonia, having addedthereto about 0.05 to 0.25 gram/100 ml. of said solution of AS303, about0.01 to 0.2 gram/100 m1. of said solution of basic copper carbonate, andabout 0.05 to 0.25 gram/100 ml. of said solution of sodium hydroxide.

8. The composition of claim 7 wherein the amount of basic coppercarbonate is about 0.05 to 0.15 gram/100 ml. of said solution.

9. The composition of claim 7 having added thereto a small, eliectiveamount of sodium nitrite as a vapor phase corrosion inhibitor.

10. A composition consisting essentially of an aqueous ammoniacalammonium nitrate solution, about 0.01 to less than about 0.5 gram/100ml. of said solution of an inorganic tri-valent arsenic compound solublein said solution, about 0.01 to 0.2 gram/1'00 ml. of said solution of acopper compound soluble in said solution, and about .005 to .1 gram/100ml. of said solution of carbonate ions, the amounts of said compoundsand ions being sufficient to substantially reduce the rate of corrosionby said solution to ferrous surfaces.

11. The composition of claim 10 wherein the copper compound is aninorganic copper compound.

12. The composition of claim 11 wherein the ammoniacal ammonium nitratesolution is of about 1 to ammonium nitrate, about 5 to 35% ammonia withthe substantial balance being water and the concentration of thetrivalent arsenic compound is about 0.01 to 0.5 gram/ ml. of saidsolution, the concentration of the inorganic copper compound is about0.01 to 0.2 gram/ 100 ml. of said solution and the concentration of thecarbonate ions is about 0.005 to 0.1 gram/100 ml. of said solution.

13. The composition of claim 12 wherein the copper and carbonate ionsare supplied by the addition of about 0.01 to 0.2 gram/100 ml. of saidsolution of basic copper carbonate.

14. The composition of claim 13 in which the trivalent arsenic compoundis arsenic trioxide.

15. The composition of claim 12 in which there is included about 0.01 to0.5 gram/said solution of alkali metal hydroxide.

16. The composition of claim 15 in which the hydroxide is sodiumhydroxide.

References Cited in the file of this patent UNITED STATES PATENTS

1. A COMPOSITION CONSISTING ESSENTIALLY OF AN AQUEOUS AMMONIACALAMMONIUM NITRATE SOLUTION, ABOUT 0.01 GRAM TO LESS THAN ABOUT 0.5 G./100ML. OF SAID SOLUTION OF A TRIVALENT ARSENIC COMPOUND, SOLUBLE IN SAIDSOLUTION, ABOUT 0.01 TO ABOUT 0.2 GRAM/100 ML. OF SAID SOLUTION OF ACOPPER COMPOUND SOLUBLE IN SAID SOLUTION, AND ABOUT .005 TO .1 GRAM/100ML. OF SAID SOLUTION OF CARBONAATE IONS, THE AMOUNTS OF SAID COMPOUNDSAND IONS BEING SUFFICIENT TO SUBSTANTIALLY REDUCE THE RATE OF CORROSIONBY SAID SOLUTION TO FERROUS SURFACES.